Solid-state lighting (SSL) devices, such as light-emitting diodes (LEDs), are used in current lighting systems. These LEDs provide light at a certain wavelength. in order to operate the lamp with different colors, differently colored LEDs are assembled within one single lamp. The LEDs, when operated, provide the primary colors, which are superposed to create the output color of the lamp.
The LEDs may define an area within the color space indicating the color that can be realized by the lamp through linear combinations of the fluxes of the LEDs. Adjusting the flux of each LED so as to contribute to the overall color of the lamp is known in the art for lamps comprising three LEDs. It is known that there is an exact relation between a target color point, for example defined by tristimulus values (Xt, Yt, Zt), and the average flux Φ of three primary colors. It is also known that the average flux Φ can be defined by the duration a LED is operated. For example, in pulse width modulation (PWM) based systems, the average flux Φi, of the ith, color can be given by Φi={circumflex over (Φ)}ipi, with pi, representing the duty cycle (duration of operation in one period divided by total length of period) of the ith, primary color and {circumflex over (Φ)}i, the peak value of the flux. Within a three-color system, i.e. lamps with three different primary colors, the duty cycle for each of the primary colors required for obtaining one given color point can thus be calculated.
However, it is not possible in the art to calculate the contribution of a primary color to obtain a target color point if more than three primary colors are used in a lamp.
Therefore, it is a first object of the present patent application to provide an easy color point calculation. Another object of the present patent application is to provide a lamp, which emits light with a high color-rendering index. Another object of the present patent application is to provide an easy implementation of color point calculation. Another object of the present patent application is to provide a color point calculation using pulse width modulated systems.